Welding transformer control system



Feb. 6, 1951 H. w. SNYDER 2,540,837

WELDING TRANSFORMER CONTROL SYSTEM Filed March 29, 1946 3 1 2T7; A? o 6amigo a a I 7 6 a /7 /a c divs-4 INVENTOR Patented Feb. 6, 1951 WELDINGTRANSFORMER CONTROL SYSTEM Henry W. Snyder, West Allis, Wis., asslgnorto Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporationof Delaware Application March 29, 1946, Serial No. 658,047

3 Claims. 1

This invention relates in general to improvements in control systems forwelding transformers, and more particularly to means for reducing thevoltage of a welding transformer while the transformer is not carryingload current.

The supply of alternating current to welding electrodes is frequentlyeffected through a transformer having a secondary open circuit voltageof such magnitude as to constitute, under favorable circumstances, asubstantial hazard to a human being touching both electrodessimultaneously. It is therefore desirable to energize the transformer atreduced voltage while the transformer is not carrying load current. Forthe latter purpose, it is advantageous from the point of view ofsimplicity and economy of equipment to energize the transformer atreduced voltage through the actuating coil of the switch serving for thedirect connection of the transformer with the source upon engagement ofthe welding electrodes. The reduced voltage may be impressed on thewelding transformer from the source through suitable transformer means,which may consist of an autotransformer of low cost as the weldingtransformer need not be insulated from the source. Contactor coils ofstandard construction may be utilized for the control of different typesof welding transformers by suitably choosing the connections between thecoil, the welding transformer and the autotransformer.

It is therefore an object of the present invention to provide animproved system for causing the open circuit voltage of a weldingtransformer to be reduced by simple and inexpensive means.

Another object of the present invention is to provide an improved systemfor reducing the open circuit voltage of a welding transformer which isadapted for the control of transformers supplied from sources ofdifferent voltages.

Another object of the present invention is to provide an improved systemfor reducing the open circuit voltage of a welding transformer whichpermits utilizing elements of standard construction for controllingdifferent tyeps of welding transformers.

Objects and advantages other than those above set forth will be apparentfrom a consideration of the following description when read inconnection with the accompanying drawing, in which:

Fig. 1 diagrammatically illustrates one embodiment of the presentinvention applied to the control of a welding transformer provided withan undivided primary winding;

Fig. 2 diagrammatically illustrates a modified embodiment of the presentinvention applied to the control of the welding transformer providedwith a tapped primary winding; and

Fig. 3 diagrammatically illustrates another modified embodiment of thepresent invention applied to the control of a welding transformerprovided with a primary winding adapted to be energized at voltages ofdifferent values.

Referring more particularly to the drawing by characters of reference,numeral 6 generally designates a welding transformer of any known typeprovided with a primary winding 6a and a secondary winding 6b. Winding6b is connected with a welding circuit 1 for supplying current to a pairof welding electrodes 8, 8 of which electrode 8 is assumed to be a rodof weld metal and electrode 9 the work to be welded. The flow of currentthrough electrodes 8, 9 is adjustably limited by causing the path ofsuch flow of current to have a substantial variable impedance, as iswell known. The latter result may be obtained by so disposing windings6a, 6b as to cause the leakage reactance thereof to have a substantialvalue or by connecting winding- 6b with circuit 1 through impedancemeans such as an adjustable reactor I l of any suitable type. I

Terminals 6c, 8d of winding 6a are to be connected with a suitablesource of alternating current such as a circuit 12 energized from asuitable generator (not shown) through connections which may includedisconnecting switches l3 and the main contacts Mb of a contactor switchl4. If it is desired to raise the power factor of the current suppliedfrom circuit l2 to the system, switch I4 may be provided with furthercontacts I40 for connecting a capacitor H in parallel with winding 6a. Adischarge resistor l6 may be connectcd across capacitor IS.

The actuating coil I 4a of switch [4 may be energized from circuit ii.at reduced voltage through any suitable transforme means. No insulation,however, need be provided between coil Ma and circuit I2 and thetransformer means may therefore advantageously be in the form of anautotransformer H. The terminals Ila, llb of the autotransformer areconnected with circuit 12 through switches 13, and a fixed or adjustabletap l'lc thereof is connected with terminal 6d through coil Ma andcontacts Nb of a relay Hi. The coil l8a of relay I8 is connected acrosscircuit I to cause relay l8 to open contacts I8b in response to rise ofthe voltage of circuit 1 to a value substantially in excess of the valuethereof resulting from establishment of an are between electrodes 8, 9.The speed of operation of relay l8 may be established at any desiredvalue by proper choice of 3 the relay elements, which may include anysuitable known delaying means conventionally represented as a dashpotIBc.

In operation, circuit I2 being energized and switches I3 being closed,the full voltage of circuit I2 is impressed across terminals Ila, III).A reduced voltage at value depending upon the choice of tap He is thenimpressed from the autotransformer on the circuit extending from tapI'Ic through coil Ila, contacts Ito and winding la to terminal Ill). Theflow of current through winding 6a causes winding 6b to impress apredetermined reduced voltage on electrodes 8, 8. Tap Ho and theimpedance of coil Ila are so chosen that the flow of current through thecoil is insufiicient to cause switch Il to close its contacts and thatthe voltage appearing across the welding electrodes is of such low valueas not to constitute a substantial hazard to human life. The electrodevoltage is also insuillcient to cause operation of relay '8.

Welding operation may be initiated by-bringing electrode 8 in contactwith electrode 9. A substantial current then flows through circuit I,thereby causing the flow of current through coil Ila and winding to toincrease to an extent sufiicient to cause switch I l to close thecontacts thereof. Contacts Ilb connect terminal id with circuit I! tocause winding la to become energized at the full voltage of circuit I2.Coil I la, however. remains energized at the proper voltage to maintaincontacts Ilb. Ilc closed without overheating as a result of theconnection of the coil between terminal IIa and tap IIc through contactsIlb and ilb. Contacts Ilc connect capacitor II across circuit I! toraise the power factor of the current supplied therefrom to the weldingtransformer. Electrodes l, 8 may then be separated to draw a welding arctherebetween.

The are voltage is however insumclent to cause operation of relay it,which remains in the position shown.

When the flow of current through winding 6b is interrupted by separationof electrodes 8, 9 beyond a predetermined distance, the voltage ofcircuit I abruptly increases to a predetermined value which may beconsidered to constitute a hazard to human life. After a predeterminedtime delay, relay it opens contacts ill) to deenergize coil Ila. SwitchIl returns to the position shown to disconnect terminal to from circuitI2. Contacts Ilb being open, winding 8a is at first open circuited sothat circuit I is deenergized and relay It returns to the positionshown. Upon reclosure of contacts I8b, transformer l is again energizedat reduced voltage and another welding operation may be initiated byengagement of electrodes 8, 9.

In the embodiment illustrated in Fig. 2. winding la is assumed to beprovided with an intermediate terminal or tap 6e. While no power factorcorrection capacitor is shown in Fig. 2 it will be understood that suchcapacitor may be connected between terminals to, 6d either directly orthrough suitable contacts of switch Il. Coil Ila may be connected eitherwith terminal is or with terminal id to obtain impression of the desiredreduced voltage on winding la through coil Ila and to cause the currentof coil Ila to assume the desired values when circuit I is opencircuited and short circuited. To permit a greater latitude in thechoice of coil Ila and of tap I'Ic, coil Ila is connected with terminalle through contacts Ild of switch Il when the switch is in the positionshown and the coil is conne ted with terminal to through contacts lle,Ilb when the switch is actuated.

The operation of the embodiment illustrated in Fig. 2 is generallysimilar to that of the embodiment illustrated in Fig. 1. When switch I lis actuated, however. contacts Ild open to disconnect coil Ila fromterminal is and contacts Ile close to reconnect coil Ila with terminalto through contacts Ilb. The current of coil Ila may thus be maintainedmore easily within the ranges of value resulting in operation ornonoperation of switch Il in response to short circuiting or opencircuiting of circuit I.

In the embodiment illustrated in Fig. 8, welding circuit I is assumed tobe energised from a transformer It adapted to be supplied from circuitsoperating at diiferent voltages. Transformer I! is provided with aprimary winding its associated with two parallel secondary windings Itb.llc. Winding Ila is provided with: plurality of terminals Ild, Ile, It!and Ila. Circuit I2 may be connected between terminals III- Ilg orbetween terminals Ild, ile depending on the value of the voltage ofcircuit It. Capacitor I5 is preferably connected between terminals ltd.lie to obtain full utilization of the capacitor rating.

Autotransformer I1 is replaced by an autotransformer II provided with anadditional tap 2Id. A selector switch permits connecting circuit itbetween terminals Ila, lib or between terminal 2ia and tap lid dependingupon the voltage of circuit I2. Coil Ila may be connected throughcontacts Ild with any of terminals ltd, Ile, Ila depending upon theamount of current required for energizing transformer II at reducedvoltage and upon the amount of current required for causing operation ofswitch Il. The voltage of portion a--c o'f autotransformer ii is thusimpressed on a selected portion of winding its to cause energization ofcircuit 1 at reduced voltage. The operation of the embodimentillustrated in Fig. 3 is otherwise identical to that of the embodimentillustrated in Fig. 2.

Although but a few embodiments of the present invention havebeenillustrated and described. it will be apparent to one skilled in the artthat various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent: I

1. In a control system for a welding transformer comprising a primarywinding provided with first and second terminals to be connected to asource of alternating current and a secondary winding having a normalopen circuit voltage of dangerously high value connected to a weldingcircuit, the combination of transformer means connected with said sourceand impressed with the voltage thereof to produce a reduced voltage, aconnection joining said first terminal with said source and saidtransformer means. a switch for connecting said second terminal withsaid source, said switch being provided with an actuating coil, aconnection between said second terminal and said transformer meansthrough said coil to impress said reduced voltage between said terminalsto cause the open circuit voltage of said secondary winding to bereduced to a predetermined value and cause closure of said switch inresponse to short cireuiting of said welding circuit, and meansresponsive to closing operation of said switch for disconnecting saidcoil from said second terminal and reconnecting said coil with saidfirst terminal.

2. In a control system for a welding transformer comprising a primarywinding provided with first and second terminals to be connected to asource of alternating current and a secondary winding having a normalopen circuit voltage of dangerously high value connected to a weldingcircuit, the combination of transformer mean connected with said sourceand impressed with the voltage thereof to produce a reduced voltage, aconnection joining said first terminal with said source and saidtransformer means, a switch for connecting said second terminal withsaid source, said switch being provided with an actuating coil, 9,connection between said second terminal and said transformer meansthrough sa d coil to impress said reduced voltage between said terminalsto cause the open circuit voltage of said secondary winding tobe reducedto a predetermined value and cause closure of said switch in response toshort circuiting of said welding circuit, means responsive to closingoperation of said switch for disconnecting said coil from said secondterminal and reconnecting said coil with said first terminal, and arelay provided with a coil connected with said welding circuitresponsive to rise of the voltage of said welding circuit above saidpredetermined value for opening said connection between said transformermeans and said first terminal through said coil.

3. In a control system for a welding transformer comprising a primarywinding provided with a plurality of terminals, certain of saidterminals to be connected to a source of alternating current, and asecondary winding having a normal open c rcuit voltage of a dangerouslyhigh value connected to a welding circuit, the combination of anautotransformer connected with said source and having a reduced voltagetap, means joining a first said terminal with said autotransformer andwith said source, a switch for connecting a second said terminal withsaid source. said switch being provided with an actuating coil, aconnection between said tap and one of said terminals other than saidfirst terminal through said coil to impress said reduced voltage on apredetermined portion of said primary winding to cause the open circuitvoltage of said secondary winding to be reduced to a predetermined valueand cause closure of said switch in response to short circuiting of saidwelding circuit, and means responsive to operation of said switch foropening said connection through said coil and for reconnecting said tapwith said first terminal through said coil.

HENRY W. SNYDER.

REFERENCES CITED The following references are of record in the file orthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date France May 8, 1933Number Number

